I actually like the tones I've gotten out of class d markbass gear. Granted, it was at GC volume levels.
I'm trending in the other direction. I may just end up with an SVT and a fridge. Every damn time I play an SVT it's 100% what I want sound-wise.
I've owned a hybrid class D amp, multitudes of solid state and tube amps. I'm a pretty clever monkey, and understand a lot about electronics. But, I'm not an engineer, so take this with a grain of salt.
I haul around the Super Bassman because it's the one that sounds the best and has the watts to handle the shows. Tube amps just compress more smoothly, in a way you don't really notice as controlling your volume. It's not transparent, but tends to distort in a pretty pleasing way when you drive it even a little bit.
Some non-class D solid state power amps distort in a pleasing way, but the designer generally has to be pretty conscious of it to make it happen. It's more common for a solid state power amp to distort in a less pleasing way when you drive it - so the compression it provides is different from a tube amp, even if the engineer really knew what he was doing. Some people prefer the compression provided by certain solid state designs. I like them a lot myself, even on guitar.
Every class D power amp's specs I've looked at pretty much doesn't distort until you've got the master wayyyy past what you're likely to use. So you don't get much natural compression, and you've got to be pretty much spot on with your dynamics for it to sound nice and even. Now, I'm pretty much saying you have to be a better bass player than me to make a class D sound really good - and that's somewhat true. This compression could happen earlier in my signal chain, but I prefer it to happen in the power amp because it compresses everything before it. So, I carry around a boat anchor.
But! I have been eyeing a Bassman 500, since sometimes the house is big enough that I'm pretty certain everyone's hearing the PA instead of my power amp, and it's got the same preamp and direct out. Those gigs also seem to always be the ones where parking is frigging stupid. If no one's going to hear my power amp, anyway, why carry it a block?
Edit: But I'm not carrying around anything bigger than a 410 HLF. 8x10s are for guys with roadies.
tl;dr: It's a matter of taste, but it's hard to beat tube power amps for some situations.